Rated 5 out of 5 stars

Simply updating the install.rdf file by changing the maxVersion to 4.0.0.* fails for me: FF3 on Win Vista. Absolutely great extension, though.

This review is for a previous version of the add-on (0.9.15.11). 

that version 4.0.0.* is unacceptable. Try using:
minVersion=2.0
maxVersion=3.0.*

Alternatively... try at the project download page.
http://googlebar.mozdev.org/installation.html